DESCRIPTION (Verbatim From the Applicant's Abstract): The primary means by which nerve cells communicate with each other is through the release of neurotransmitter at chemical synapses. The ability of the brain to process information depends on synaptic connections forming precisely and reliably between hundreds of different types of neurons. This application is directed towards developing a molecular understanding of processes that regulate synapse formation. We have created synaptic vesicle protein-GFP fusions and expressed these in subsets of glutamatergic mechanosensory neurons in the nematode C. elegans enabling us to visualize presynaptic specializations at light level resolution in live animals. Using these transgenic animals, we have isolated mutants of C. elegans that are compromised in their ability to form interneuronal synaptic specializations. We propose to further analyze these mutants, particularly concentrating on ultrastructural characterization of abnormalities associated with the genetic lesions. Secondly, we propose molecular cloning of the genes lesioned in several of these mutants. Molecular cloning of the first of these genes suggests it encodes a large protein with homology to a protein expressed in the vertebrate brain. Thirdly, we propose the detailed molecular genetic characterization of the gene products identified through our genetic analyses to assess their roles in the process of synapse development. While synaptogenesis in C. elegans likely is less complex than in vertebrates, analysis of the molecules participating in the process in C. elegans should lay a basic scaffold on which to integrate the complexities associated with more general and likely conserved principles of synaptic development.